This invention relates to a graphics display apparatus incorporating a graphics processor and a bit-per-pel refresh buffer.
The invention is particularly useful in a display apparatus incorporating a color cathode ray tube in which three planes of refresh buffer contain red, blue and green bit patterns. The refresh buffer is periodically scanned by refresh logic to produce bit streams that turn the red, green and blue electron beams on and off as they are raster scanned across the screen of the CRT. The bit pattern stored in the refresh buffer is loaded therein under control of a graphics processor which is a mixture of hardware and software.
Early graphic display apparatus were usually driven from large central processing units but more modern graphics displays employ microprocessors. The use of software routines generally slows down the creation of the bit patterns in the refresh buffer and, although this was not previously a problem with large processors (because of their processing speeds), it is a problem when using less powerful processors to drive the displays. To this end it has previously been proposed to employ special purpose or dedicated hardware to assist in the drawing of vectors and arcs in the refresh buffer.